ADM1029ARQZ-R7 datasheet(19/50 Pages) ONSEMI

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ADM1029

spin the fan up for a predetermined time, and once the fan has

spun up, its running speed may be reduced in line with the

temperature being measured.

The ADM1029 allows fan spin-up times between 1/64 second

and 16 seconds. The Fan Spin-Up Register (Register 0x0C)

allows the spin-up time for the fans to be programmed. Bit 3

of this register, when set, disables fan spin-up for both fans.

Table V. Fan Spin-Up Times

Spin-Up Times

Bits 2:0

(Fan Spin-Up Register)

000

16 Seconds

001

8 Seconds

010

4 Seconds

011

2 Seconds (Default)

100

1 Second

101

1/4 Second

110

1/16 Second

111

1/64 Second

Once the Automatic Fan Speed Control Loop parameters have

been chosen, the ADM1029 device may be programmed. The

ADM1029 is placed into Automatic Fan Speed Control Mode

by writing to the three Temperature Cooling Action Registers

(Registers 0x48, 0x49, 0x4A). The device powers up in Auto-

matic Fan Speed Control Mode by default, as long as the TMIN/

Install pin (Pin 18) does not have the disable option selected

(TMIN/Install pin tied low or high). The default setting is that

both fans will run at the fastest speed calculated by all three

temperature channels. The control mode offers flexibility in that

the user can decide which temperature channel/channels control

each fan (five options).

Table VI. Automatic Mode Fan Behavior

Option

Temperature Cooling Action

Bit 0 Register 0x49 and/or Bit 1 Reg 0x4A =

Remote Temp 1 Controls Fan 1, Remote Temp 2

Controls Fan 2

Bit 0 Register 0x48 and Bit 1 Register 0x48 = 1

Local Temp Controls Fan 1 and/or Fan 2

Bit 0 Register 0x49 and Bit 1 Register 0x49 =

Remote Temp 1 Controls Fan 1 and/or Fan 2

Bit 0 Register 0x4A and Bit 1 Register 0x4A =

Remote Temp 2 Controls Fan 1 and/or Fan 2

Bits 0, 1 Reg 0x48, 0x49, 0x4A = 1 Max Speed

Calculated by Local and Remote Temperature

Channels Controls Fans 1 and/or 2

When Option 5 is chosen, this offers increased flexibility. The

Local and Remote temperature channels can have independently

programmed control loops with different control parameters.

Whichever control loop calculates the fastest fan speed based on

the temperature being measured, drives both fans.

Figure 13 shows how the fan’s PWM duty cycle is determined

by two independent control loops. This is the type of Automode

Fan Behavior seen when Bits 0 and 1 of all three Temperature

Cooling Action Registers = 11. Figure 13a shows the control

loop for the Local Temperature channel. Its TMIN value has

been programmed to 20°C, and its TRANGE value is 40°C.

T R

REMOTE TEMPERATURE

– C

TMIN

TMAX = TMIN + TRANGE

100

LOCAL TEMPERATURE

– C

TMIN

TMAX = TMIN + TRANGE

100

Figure 13. Max Speed Calculated by Local and Remote

Temperature Control Loops Drives Fans

The local temperature’s TMAX will thus be 60°C. Figure 13b

shows the control loop for the Remote 1 Temperature channel. Its

TMIN value has been set to 0°C, while its TRANGE = 80°C. There-

fore, the Remote 1 Temperature’s TMAX value will be 80°C.

If both temperature channels measure 40°C, both control

loops will calculate a PWM duty cycle of 66%. Therefore, the

fans will be driven at 66% duty cycle.

If both temperature channels measure 20°C, the local channel

will calculate 33% PWM duty cycle, while the Remote 1

channel will calculate 50% PWM duty cycle. Thus, the fans will

be driven at 50% PWM duty cycle. Consider the local temperature

measuring 60°C, while the Remote 1 temperature is measuring

70°C. The PWM duty cycle calculated by the local temperature

control loop will be 100% (since the temperature = TMAX). The

PWM duty cycle calculated by the Remote 1 temperature

control loop at 70°C will be approximately 90%. So the fans will

run full speed (100% duty cycle). Remember that the fan speed

will be based on the fastest speed calculated, and is not necessarily

based on the highest temperature measured. Depending on the

control loop parameters programmed, a lower temperature on one

channel may actually calculate a faster speed than a higher

temperature on another channel.

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